Many people have shared their thoughts on how thy want RDM to be, so I won't need to add more. However, I have my own idea of what "Jack of all Trades" should be. We should not be reducing the direct POTENCY of a RDM's abilities, but rather limit its availability. Let me give you some examples:

Healing: Give them a Cure that heals the same as a WHM. Also give them Raise and AoE Heal that does the same as Medica. But do not give them shields, regen, Divine Seal, Lustrate, or any those specialized spells. Over time they are less efficient as a healer, but their heals will have the same potency as an individual WHM Cure.

Damage: Give them the ability to go to Astral III and Umbral III and thus deals the same damage as BLM with Fire I and Fire II, but don't give them spells that automatically take them there like Fire III and Blizzard III. Give them all dots like Bio I, Miasma I, Aero I, and Thunder I.

(word limit, continued below)